1. Field of the Invention
This invention relates to communications and other electronics systems which utilize antennas which are exposed to lightning and similar environmental disturbances and more particularly to lightning protection apparatus for such systems.
2. Description of the Prior Art
Receiving and transmitting antennas for radio and other RF equipment are often positioned as high as possible above the ground and are usually arranged to be above trees and other structures. Accordingly, they are very likely to attract lightning strokes or to be affected by near misses. When the antenna is struck by lightning or is even subject to a near miss, a surge of current of a very high order of magnitude is induced in the antenna and transmitted to the RF equipment to which the antenna is coupled. Needless to say, it is necessary to protect RF equipment from the high current and voltages to which they may be subjected by such atmospheric events.
Lightning usually consists of one or more pulses having a short rise time and a long decay time. The currents induced by lightning could range into the thousands of amperes. One known method of protecting against current and voltage surges is a series circuit breaker. This may take several forms, such as a fuse, an electromechanical circuit breaker or a self-triggering solid state circuit breaker, for example. Unfortunately, each of these devices has a relatively long operating time delay which may permit the equipment being protected to be damaged. Additionally, these devices disturb the operation of the equipment being protected by preventing operation of the equipment until the device is repaired or reset. Another method of protecting antenna coupled RF equipment is to employ a shunt or bypass device that would either disipate the energy of the lightning stroke or bypass it to ground. Many of these devices are also subject to the operating time delay and need to repair/reset ills to which the series circuit breaker devices are subject. A third method of protection is the tuned or selective type of protection system which will allow only the desired RF signals or "traffic" to flow to/from the antenna but will divert or bypass the harmful energy of the lightning occurrence. It is this method with which the present invention is concerned.